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Topic: Tilt Switch and 555 Timer Astable Circuit for LED (Read 4747 times) previous topic - next topic

ted


jarus

In this arrangement 30sec start from last acceleration - it is ok ?
Yes, that's fine.
I can do that later - 1.5 hour
Thanks, I appreciate it. 555 is attached to Source? I can wait for the drawing.

ted


ted


jarus


jarus

I am back, drawing is coming soon
Thanks for the drawing! I built the circuit after figuring out what components to use. I have attached a circuit diagram of what I have built.

The LED is not bright. I attached an ammeter from the LED to ground terminal and it was only drawing 20mA and 1.7V accross the LED with the 4.7 Ohm, 1W resistor. So I removed the resistor and measured the current from the 555's output pin 3 to ground and it was around 200mA (as the spec sheet states) and 2.9V. So then I connected the LED to pin 3 and ground with no resistor but it was still only drawing 20mA. I'm confused...

ted

Not like that.
You need another MOSFET for LED, Drain of second MOSFET connect to source of the first one, source to LED, gate to R2, make R2 bigger 1- 10k.
Your LED is 2.1V so add one more in series with it.

jarus

Not like that.
You need another MOSFET for LED, Drain of second MOSFET connect to source of the first one, source to LED, gate to R2, make R2 bigger 1- 10k.
Your LED is 2.1V so add one more in series with it.
Okay how's this? Also can you explain why another MOSFET is needed? Is it bc it is faster at switching?

And I'm assuming you recommended 2 LEDs bc the supply voltage is 4.5V?

Thanks!

Wawa

Sorry, but I think ted needs to learn more about mosfets before posting diagrams like this.

The circuit posted uses an N-channel mosfet (2N7000, BUK9520) as source follower.
It means that source is always Vg(th) lower than the gate.
I doubt that an NE555 (4.5volt minimum), and two LEDs in series, will run correctly on a ~2.5-3volt supply.

If you want to power the NE555 high-side through a mosfet switch, you must use a p-channel fet (source to battery/VCC),
with the switch and RC circuit swapped (switch between gate and ground, and RC between VCC and gate).

The NE555 also needs some decoupling on it's supply pin.
Leo..

ted

The LED is not bright. I attached an ammeter from the LED to ground terminal and it was only drawing 20mA

= first MOSFET is working, and he is learning.


ted

The circuit is ok, AA battery will not last long, duracell battery are the strongest one, consider 18650 3.7 Volt Lithium Ion Battery, you need to check that, will this circuit work at lower voltage in practice, regardless what data sheet is telling.
Do you have 30 sec ?

jarus

Sorry, but I think ted needs to learn more about mosfets before posting diagrams like this.

The circuit posted uses an N-channel mosfet (2N7000, BUK9520) as source follower.
It means that source is always Vg(th) lower than the gate.
I doubt that an NE555 (4.5volt minimum), and two LEDs in series, will run correctly on a ~2.5-3volt supply.

If you want to power the NE555 high-side through a mosfet switch, you must use a p-channel fet (source to battery/VCC),
with the switch and RC circuit swapped (switch between gate and ground, and RC between VCC and gate).

The NE555 also needs some decoupling on it's supply pin.
Leo..
Hi Leo,

What I am learning is to use N-Channel if between load and ground and P-Channel if between positive and load. So the N-channel could have worked if drain was connected to ground? Correct?

For decoupling of the 555, does that mean a capacitor between drain and ground? It's C3 in the diagram but I don't know to calculate it's capacitance.

How do you recommend switching/powering the LED? Do I still need a MOFSET as Ted recommended? And I am guessing it should be a P-channel if so?

Think I should look into MOSFETS with a lower Vg(th) (currently 2V) and a 555 IC with lower operating voltage (maybe LCM555 or TLC555)? I'd like to power this thing with the minimum number of AA batteries. Right now I will need 2V (Vgth) + 4.5V (555)

jarus

The circuit is ok, AA battery will not last long, duracell battery are the strongest one, consider 18650 3.7 Volt Lithium Ion Battery, you need to check that, will this circuit work at lower voltage in practice, regardless what data sheet is telling.
Do you have 30 sec ?
Thanks I will look into that battery. The circuit will be activated around 10x per month with the LED flashing at 4hz for 30 seconds @350mA.

I am afraid of using another MOFSET due to the drop of voltage...Then I will need a higher voltage battery pack Vss.

I had calculated the RC circuit to be timed to 30 seconds - but this did not work in practice. It was much shorter. So I will have to adjust the R as you mentioned until I get the desired timing.

ted

If it is 10x a month you don't need to change batteries.
Calculation can be ok but components not, capacitors not always have the value as is it say on it, increase R1.
Leave  MOSFET as is, just connect everything and observe what is happends.
When you make a drawing dont use description  - Pin1, just 1, thats what is in practice, ehen you describe something in text, use Pin1

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